Vacuum tube isolator,circuit protector,and voltage regulator



5. SCHNEIDER ETAL VACUUM TUBE ISOLATOR, CIRCUIT PROTECTOR, AND VOLTAGEREGULATOR Filed Jan. 15, 1969 A E a 10A 108 PowER 4 40B SUPPLY ENERGY LENERGY STORAGE STORAGE 30A- ,308

ENERGY ENERGY ENERGY DIVERTER DIVERTER STORAGE FIG. 1 (PRIOR ART) 6O\ 6POWER -L FUSE CIRCUIT BREAKER 4O SUPPLY I 42 3o ENERGY 22 20 L 243 FIG.2 (PRIOR ART) so clRculT BREAKER POWER SUPPLY CONTROL CIRCUIT ENERGYSTORAGE 30 ENERGY DIVERTER RF TUBE i'ad X If -61 AGENT AT TORNE Y8United States Patent 3,539,870 VACUUM TUBE ISOLATOR, CIRCUIT PROTEC-TOR, AND VOLTAGE REGULATOR Sol Schneider, Little Silver, and George W.Taylor, Brielle, N.J., assignors to the United States of America asrepresented by the Secretary of the Army Filed Jan. 15, 1969, Ser. No.791,459 Int. Cl. H02h 7/20 US. Cl. 317-51 4 Claims ABSTRACT OF THEDISCLOSURE This disclosure relates to energy control and particularly toenergy control in the form of isolation and protection for multiple,amplifier circuits operating from a common power source. Moreparticularly, this disclosure is of the use of vacuum tubes as switchesfor isolating and protecting individual pulse-amplifier circuits orunits of a multiple-unit system having a common power supply. Thisdisclosure teaches the connection of a vacuum tube to each of thecircuits to switch it off when the circuit faults or short circuits andto switch the circuit back on when the fault clears itself. This avoidsdraining the main capacitor bank through the short-circuit, which coulddamage the individual circuit and interfere with the operation of othercircuits using the same, common, power supply. The system also providesregulation of voltage to the individual circuits to increase theirefficiency.

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto us of any royalty thereon.

BACKGROUND OF THE INVENTION This circuit isolator was invented to meetthe problems of power supplies for super power systems with pulseamplifiers for microwave pulse transmission. These systems, as the nameimplies, involve units of comparatively large size that handle voltagesand currents, during a pulse transmission, that are considerably inexcess of those encountered in conventional transmitters. The problemsin super power pulse transmission systems are predictable. The voltagesand currents involved are of values that approach the limits ofconventional electronic circuitry. The RF tubes, themselves, areoperating under conditions that make faulting or failure of the tube anunavoidable possibility. Then, too, the power surges that accompany suchfaulting are of a magnitude that can completely destroy the RF tube orother elements in the circuit involved, particularly when the powersupply includes a large capacitor bank for energy storage.

This circuit isolator is particularly needed in systems where aplurality of pulse transmitters are required and are supplied by asingle power supply. Such a situation occurs with a phased-array radarwhich has an extremely large antenna with many radiating elements, eachpowered by a separate pulse transmitter. The transmitters may all befired together or may be fired in any sequence or phase necessary tohave the desired effect on the transmitted beam. The problem is toprovide protection for the individual pulse transmitters against shortcircuits and to minimize the damage attended on a fault in any one ofthe separate transmitters and, in any case, to keep the othertransmitters operating with as little disturbance as possible during afault of one of the units.

One solution would be to provide a separate power supply for each of thepulse transmitters. This would solve the problem of isolation but wouldbe prohibitively expensive because of the cost and size of the separatepower supplies. This would also be ineflicient and would not reduce thepossibility of damage to any one of the units. It is more desirable andmore efficient to have a single, common, power supply serving all of thepulse transmitter units. This power supply would include a main energystorage device in the form of a capacitor bank of suflicient capacity tosupply the instantaneous power requirement of the entire system.Additional energy storage banks are also connected to each, individualpulse transmitter to provide the instantaneous energy needed duringpulse transmissions at the actual location of the pulse transmitter toprevent jitter and electronic beam path instability due to the length ofthe lines between the main energy storage bank and the individual pulsetransmitters.

When the systems are operating from a common power supply, each of thepulse transmitters is connected to the common power supply through anisolator. Isolators are usually used with each individual circuit tostop the discharge of the main capacitor bank until the secondarycapacitor bank is discharged and the fault is cleared.

The isolator can take various forms, the most common form having passivecomponents which may be merely a high voltage fuse with a backup circuitbreaker. In the event of a fault the fuse would blow and the circuitbreaker would open. The discharge current in the fuse would be quenchedby sand or other medium in a well known manner.

The passive component isolator has the serious disad- 'vantage ofinactivating the circuit until the fuse is replaced and is tolerableonly if faulting rarely occurs or if the system can operate effectivelywithout some of the pulse transmitters. There is also a question as towhether the fuse could open quickly enough to avoid a surge of currentthat might be enough to destroy the pulse transmitter or to effect thestability of the common power supply.

A vacuum tube type of switch connected in series with each of the pulsetransmitters would be one way of interrupting the flow of current fromthe main capacitor bank and isolating the individual transmitters. Inthe event of a fault the vacuum tube could be switched off, therebyinterrupting energy flow and providing protection for the pulsetransmitter. After the fault clears, the vacuum tube could beautomatically switched on again.

However, such a vacuum tube would have to be specially designed tooperate under the extremely high changes of voltage with respect to timethat would result from the transients that occur when the load faults.For example, changes in voltage with respect to time in the order of300,000 volts per microsecond could appear across such an interrupter inexisting pulse transmitters and, in all likelihood, a conventionaltriode or tetrode would are under these conditions. The tube must alsohave, for maximum efliciency, a low voltage drop, which again, is notfound in standard equipment.

Such a tube would also require low input capacitance and low drivevoltage since if the storage capacitance across the RF tube of the pulsetransmitter is removed, the vacuum tube interrupter switch must bedriven to full conduction of current in a fraction of a microsecond.Typical equivalent input capacity of vacuum switch tubes is in the orderof 1 to 4 picofarads per ampere of plate current. The grid voltage swingis in the order of 2 to 4 kilovolts for a beam current of amperes andthe turn on time of /2 microsecond. A grid drive peak current in excessof 400 amperes would be required for the best available tubes, There areno tubes presently available that can meet all these requirements.

It is therefore an object of this invention to provide an interrupterswitch for an RF pulse transmitter that can use a conventional vacuumtube.

It is a further object of this invention to provide a vacuum-tubecurrent interrupter switch and voltage regulator that can isolate acircuit from the main power supply in the event of a fault in thatcircuit to minimize the damage to the circuit during such a fault.

SUMMARY OF THE INVENTION The isolation of a pulse transmitter from acommon power supply, and the regulation of the voltage and current tothe RF amplifier tube of the pulse transmitter is achieved by connectinga high-current vacuum tube between the primary, energy-storage,capacitor bank of the common power supply and the secondaryenergy-storage capacitor bank at the pulse transmitter. The resistiveand inductive elements that are normally included are connected betweenthe secondary capacitor bank and the RF amplifier tube of the pulsetransmitter. An energy diverter with a series, limiting resistor isconnected across the RF tube itself. A voltage sensing means across theRF tube actuates a control circuit for the vacuum tube isolator andregulator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block diagram of aconventional system for connecting multiple, isolated circuits to acommon power supply;

FIG. 2 shows a single unit of such a system with a fuse type isolatorcircuit; and

FIG. 3 shows a single unit of such a system with a vacuum tube isolatorand regulator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG.1, a common power supply 6 is coupled to an energy-storage device 8which supplies several pulse amplifier circuits such as A and B. In FIG.1 each of the circuits has an isolator 10A, 10B, etc. separating theoutput loads A, 20B, etc. of the individual circuits from the commonpower supply. Each circuit normally has a secondary energy-storagedevice 40A, 40B, etc. and a diverter A, 30B, etc.

FIG. .2 shows the elements of FIG. 1 in more detail and similar elementsare similarly numbered. The common power supply 6 and the energy-storagedevice 8 supply the load which is an RF tube 20. The secondaryenergy-storagedevice is a capacitor bank 40. The RF tube has a tertiarycapacitive energy-storage device 24 and is connected across an energydiverter 30 through a current limiting resistor 22. The secondarycapacitor bank 40 supplies current to the load 20 through the resistor42 and the inductor 43 which are needed to reduce and control the flowof current during a fault discharge. Each of the units is isolated andprotected by a fuse 60 and a circuit breaker 61.

In operation, if faulting of the RF tube 20 occurs, the energy divertercircuitry senses changes in voltage or current due to the fault, andfires itself to provide a current bypass for the faulting RF tube. Thisburns out the fuse and trips the circuit breaker to disconnect thecommon power supply from the pulse transmitter circuit. The inductance43 delays the rise of fault current, and the resistor 42 limits the peakcurrent and absorbs the energy drawn by the diverter 30. The resistor 22limits the current through the RF tube itself during a fault. The fusemust be replaced, and the circuit breaker reset after the energydiverter discharges the capacitor 40 and the faulting of the RF tubeclears itself.

FIG. 3 shows this invention applied to a. circuit similar to that ofFIGS. 1 and .2, and similar elements are again, similarly numbered. Thepower supply 6 and the main, energy-storage, capacitor bank 8 supplycurrent to the RF tube 20. Additional power is available from thesecondary and tertiary capacitor banks 40 and 24 as needed. Theresistors 22 and 42 have the same function as before, as does theinductance 43. A fuse 60 and circuit breaker 61 may again be providedfor each unit, but

the main isolator or current interrupter is now the vacuum tube switch10 which may also serve as a voltage regulator.

The vacuum tube switch is, effectively, connected between the commonpower supply 6 and the secondary capacitor bank 40'. The vacuum tube isactuated by a control circuit 1 6 which is actuated by a voltage sensor26.

The operation of a system such as a phased-array radar is fairly wellknown. Such a system has a plurality of pulse transmitters including RFtubes such as 20 that are fired in a well known manner in any desiredsequence or phase. Each of the RF tubes draws current from the maincapacitor bank such as 8 of a common power supply with additionalsecondary or tertiary capacitor banks meeting the instantaneous demandsfor additional current that is necessary when the inductive effects oftoolong power lines delays the current to the individual pulsetransmitters.

In the operation of this particular isolator and regulator circuit, anyfaulting of the RF tube will appear as a short circuit with a suddencurrent surge or voltage drop which is sensed, as in the forementionedcircuit operation, by the energy diverter, which fires to bypass thecurrent away from the RF tube. However, in this circuit, the change involtage across the RF tube is also detected by the voltage sensor 26 toactuate the control circuit 16 which cuts oif the vacuum-tube switch 10.This vacuum tube switch is connected, on one side, to the common powersupply 6 whose energy storage device 8 is a capacitor bank which willvary in voltage only very slowly because of the considerable capacityinvolved. However, as pointed out earlier, if the RF tube of a pulseamplifier of a super-power system faults, changes of voltage withrespect to time in the order of 300,000 volts per microsecond or greatercan appear across any isolator and, in all likelihood, a conventionaltriode or tetrode switch tube, connected directly between the maincapacitor bank and the RF tube, would also are under these conditions.Consequently, in this circuit, the other side of the vacuum tube switch10' is connected directly to the secondary capacitor bank 40 rather thanbeing connected directly to the RF tube 20. Consequently, the voltageacross this vacuum tube switch can change only as fast as 40 isdischarged through the inductor 43 and the resistor 42 and this preventsthe high change of voltage with respect to time from appearing acrossthe vacuum-tube switch 10'. When the energy diverter completes thedischarge of capacitor bank 40 and the RF tube fault clears itself, thevoltage sensor and control circuits reactivate the vacuum-tube switch.

In this circuit, the ratio of the capacity of the secondary capacitorbank 40, the inductance 43 and resistance 42 which form the energydiverting loop through the energy diverter 30 is designed to be slightlyover-damped, rather than under-damped so that no voltage reversalsappears across the vacuum-tube switch. Since there are not extremevoltage changes, in either direction, across the vacuum-tube switch,available in triodes and tetrodes can be used with a minimum danger ofarcing.

The tube also can serve as a voltge regulator if suitable voltagesensing is incorporated in the circuit. The control circuit and inputcapacitance of triodes limits their response time. In a practicalcircuit the minimum response time will be in the order of 2 to 3microseconds. For a chain of closed spaced narrow pulses, directregulation for the individual pulses cannot be provided. However, byprogramming the control circuit, the regulator interrupter tube can bepre-pulsed to the desired operation level and since the inputcapacitance of the tube is fully charged, it can respond rapidly tosmall variations in voltage. If the control circuitry is programmed toallow the regulator tube to pass a sizeable portion of the current tothe RF tube, there are the additional advantages of increase in overallefficiency and reduction in secondary capacitance requirements. Thesecan be accomplished without any loss of voltage regulation or systemreliability but require an increase in the common power supply voltagedrop in the vacuum-tube switch.

The increase in overall system efiiciency is simply due to the decreasedenergy drained from the secondary capacitance bank. Since the secondarycapacitance is resistively charged, energy equal to the amount ofcapacitor recharge energy is dissipated during recharge. When the vacuumtube delivers energy directly from the common power supply to the RFtube the only energy loss is caused by that portion of the power supplyvoltage that represents the voltage drop in the tube. The usual vacuumtube voltage drop is approximately percent of the power supply voltage.

Only one of the pulse transmitters has been shown in FIGS. 2 and 3, forsimplicity. It is obvious, however, that any number of additional units,like the one shown in FIG. 1, are intended to be added as needed.

Sensor 26 is indicated as a voltage sensor in the embodiment of theinvention described here, since voltage sensing is an efiective mannerof actuating the control circuit. However, it should be obvious thatcurrent sensing or voltage and current sensing would be equallyapplicable here.

The vacuum-tube switch 10 may be of any available type that will carrythe current required for normal operation of the pulse transmitters. TheRF tube 20 can be similarly chosen. The values of the current limitingresistors and inductors must be chosen with respect to the currents andvoltages to be accommodated.

While the need for such isolators is clearly seen in these extremelyhigh voltages and currents of superpower amplifiers and transmitterswhere the faulting of a tube and short circuiting of a capacitor bankrepresents enormous and dangerous amounts of electrical power, thissystem is also applicable to smaller devices where the replacing of afuse is inconvenient or the sudden change of the power supply voltage isundesirable.

While we have considered here the use of vacuum-tube switches incertain, very high powered systems, it is obvious that transistors ofone kind and another may also be used here within their available poweroutput and other characteristics since it is just as possible to have afault across a transistor as a vacuum tube. Similarly, the currentinterrupter and regulator 10 may be a solid state device with suitablecontrol and voltage sensing circuits or devices.

Having described my invention, what is claimed is:

1. In combination with a power supply having a first capacitor bank, anda pulse amplifier having an output tube and a second capacitor bankconnected to said output tube through a resistor and an inductor, aprotective circuit for coupling said pulse amplifier to said powersupply comprising: a vacuum-tube switch having at least one controlelectrode; means for connecting said vacuum-tube switch between saidfirst capacitor bank and said Second capacitor bank; a voltage sensitivedevice having an input and an output; a control circuit having an inputand an output; means for connecting the input of said voltage sensitivedevice across said output load; means for connecting said output of saidvoltage sensitive device to said input of said control circuit; meansfor connecting the output of said control circuit to said controlelectrode of said vacuum-tube switch.

2. In combination with a power supply as in claim 1 a plurality of saidpulse amplifiers, each having one of said protective circuits as inclaim 1.

2. In a protective circuit as in claim 1, an energy diverter, and meansfor connecting said energy diverter across said RF tube.

4. In a protective circuit as in claim 3 said means for connecting saidenergy diverter across said RF tube including a current-limitingresistor.

References Cited UNITED STATES PATENTS 2,438,962 4/ 1948 Burlingame eta1. 3289 2,815,445 12/1957 Young et al. 3175l X 2,845,529 7/1958 Weldon328-9 3,277,342 10/1966 Ross 3l75l X JAMES D. TRAMMELL, Primary ExaminerU.S. Cl. X.R. 307108; 3289

